In the related art, for a radar device to be mounted to a moving body such as an automobile, a microstrip antenna is used as an inexpensive and small-scaled antenna, for example. The microstrip antenna includes a plurality of stacked dielectric layers, conductor layers provided on lower surfaces of the respective dielectric layers, and an antenna provided on the uppermost dielectric layer of the plurality of dielectric layers (for example, refer to Patent Document 1).
Patent Document 1: Japanese Patent Application Publication No. 2014-165529A
However, in the microstrip antenna, an electromagnetic wave may be radiated from the conductor layer. In this case, an electromagnetic wave to be radiated from the antenna and the electromagnetic wave to be radiated from the conductor layer interfere with each other, so that directionality of the antenna is badly influenced.